Researchers Trigger Memories by Stimulating Individual Neurons:
MIT researchers have shown, for the first time ever, that memories are stored in specific brain cells. By triggering a small cluster of neurons, the researchers were able to force the subject to recall a specific memory. By removing these neurons, the subject would lose that memory.
As you can imagine, the trick here is activating individual neurons, which are incredibly small and not really the kind of thing you can attach electrodes to. To do this, the researchers used optogenetics, a bleeding edge sphere of science that involves the genetic manipulation of cells so that they’re sensitive to light. These modified cells are then triggered using lasers; you drill a hole through the subject’s skull and point the laser at a small cluster of neurons.
(via MIT discovers the location of memories: Individual neurons | ExtremeTech)